1. Field of the Invention
The invention relates to a support structure for a frictional coupling device and a transmission, and particularly to a support structure that includes a snap ring for restricting the movement of a friction plate in the axial direction and a transmission incorporating such a frictional coupling device support structure.
2. Description of the Related Art
JP-A-2002-250367 describes a multi-plate clutch device that is configured to reduce the space for accommodating the clutch device. This clutch device includes first brake plates and second brake plates that are alternately arranged in the axial direction and a piston that presses the first brake plates and the second brake plates against each other, an end plate that is provided on the opposite side from the piston in the axial direction and receives the load from the piston, and a snap ring that is provided on the outer side of the end plate.
Further, JP-A-2001-193756 describes an overlap clutch assembly for an automatic transmission, which is configured to reduce its longitudinal dimension (to be compact in size) and thereby improve the accuracy in shifting the automatic transmission from the neutral position to the reverse-drive position. This clutch assembly includes clutch plates, clutch discs, a piston that is hydraulically driven in the forward direction to frictionally engage the clutch plates and the clutch discs, a stopper plate that is provided on the opposite side from the piston with respect to the clutch plates and the clutch discs, and a return spring that is provided between the stopper plate and the piston and that brings the piston back to the initial position when the clutch is released.
The frictional coupling device support structure described in JP-A-2001-193756 uses the snap ring to restrict the movement of the friction plates when they are being hydraulically driven. However, because such a snap ring is a ring-shaped member that is disconnected at a position on its circumference, that is, it is shaped like the letter “C”, not a complete ring, the rigidity at the disconnected portion of the snap ring is relatively low. Therefore, a gap may be created between the snap ring and the bottom surface of a groove in which the snap ring fits. As the hydraulic pressure applied to the friction plates acts on the snap ring repeatedly, the position of the snap ring may shift towards the outer side of the groove, and such a shift of the position of the snap ring may cause the bearing area between the snap ring and the groove to decrease to an insufficient level.